Echolocation, Echolocation, Echolocation: Your Ears are a Sight

A tree by a rock by a river, all in the fauve (wild man) style with broad brush and bright colours

Echo Rock, by Armand Guillaumin 1905

It’s well known that dolphins and bats can echolocate; they emit high-frequency sounds and can find their way around by the echoes they hear.

There are other less famous animals that can echolocate too. Some birds that live in caves where there is no light, some shrews, — and human beings! Probably there are other animals with this ability but we don’t know about them yet. But there may be a common gene for it.

To demonstrate that you can echolocate objects, here is a home experiment to try. It will work best if the background noise level is not too high.

Equipment: You.

Method: Close your eyes tightly (don’t peek!) Go “Shhhhhhh…” as though you are telling someone to be quiet (think white noise).

Now move an upright finger, or the flat of your hand, or a ball-point pen, to the right and left, at a frequency of about two sweeps per second, and at a distance of about six inches or 15 centimetres in front of your face. You should be able to hear a sound change. You can “see” with your ears.

I played with different sounds, such as the one I get when I start to say “Sue” but then stick in the “ue….”. I found that some high-pitched hisses work better than others, and that good ones let me spot a ball-point pen about a foot away. I tried different speeds of movement too. Sometimes I got a Doppler-like effect.

Naturally the experiment will be more scientific if there is someone (who doesn’t think you’re crazy doing all this!) around to help. You can get them to hold and move the objects, and then you’ll know you are not just imagining things.

So you, echolocator, are able to generate a sound and from what you hear deduce the presence of an object in front of you. Congratulations, you have joined the club!

Agreed you don’t have bat-strength skills yet. But people have been able to develop their echolocation abilities to a high level and some blind persons can use them almost as a replacement for sight.

They use clicks – like tutting, or giddying up a horse I guess – rather than shushing noises, but the basic principle is similar: You generate a sound and work out something about the surroundings from the echoes you hear.

Blind people using sound for navigation has a long history and part of the reason for tapping with a cane, as opposed just reaching out with it, must surely to get acoustic information – echoes – to help locate objects, or their absence.

Recent studies have confirmed that echolocation is real in humans and have explored how it can help the blind or near-blind There is evidence that in the case of blind people who are skilled echolocators brain areas normally devoted to visual perception have adapted to processing echolocation signals instead.

It has also been shown that people can be trained to use echolocation and that sighted people are equally capable of learning this ability, although of course they have fewer incentives.

But how does it all work? Except when in large cave-like spaces, or when the reflector is very close (as in the experiment above), you and I don’t hear any echoes (and in the experiment above they are so quick the two sounds overlap, which is what causes the change in sound quality). Why don’t we pick echoes from our near surroundings?

It’s not because echoes aren’t there: quite the contrary. But the brain filters them out. Otherwise what would it be like to talk to other people? How would you hear them but not your own voice bounced off a nearby wall?

If you have ever had the experience of an echo on Skype you will know how difficult it can make things. The reason why we can’t suppress Skype echoes but can suppress them in normal conversation is something that offers an interesting research topic.

A nice review of human echolocation, including links to further reading, is at ScienceDaily.

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About partialinsight

One evening I had a stroke. Half my sight vanished overnight. Adapting made me grasp how amazing the visual system and brain are. It also taught me to understand disability completely differently and I'm grateful for the lesson.
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